1. Field of the Invention
The present invention relates to a photovoltaic device used in solar generation of electric power, optical detection, and the like.
2. Description of Related Art
A photovoltaic device with an amorphous semiconductor as a photo-active layer is already known. It basically comprises a transparent substrate made of glass or the like, on which a lightreceiving-side electrode made from transparent conductive oxides (hereinafter denoted as TCO for short), such as ITO or SnO.sub.2, a semiconductor film having a semiconductor junction, such as pn and pin type, and a back electrode in ohmic contact with said semiconductor film, layered in this order.
Also, a photovoltaic device comprising a metallic substrate made of stainless steel or the like on which a semiconductor film with a semiconductor junction and a light-receiving-side electrode made from TCO layered in this order is known.
Almost all of the existing photovoltaic devices, in order to minimize the absorption of light in a p-type or n-type conductivity type impurity doped layer disposed on the light receiving side and obtain a higher open circuit voltage (V.sub.oc), employ hydrogenated amorphous silicon carbide (hereinafter denoted as a-SiC:H for short) having a wide band gap as this impurity doped layer. In the latest investigations, in order to obtain a still higher V.sub.oc, a film formed of hydrogenated microcrystalline silicon carbide (hereinafter described .mu.c-SiC:H for short), for example, has been tried in place of the a-SiC:H film as an impurity doped layer disposed on the light receiving side or the opposite side (H. Sasaki et al. : Proc. of Int'l PVSEC-2 pp 467-470 (Aug. 1986)).
When forming a microcrystalline impurity doped semiconductor film by a glow discharge capable of forming an amorphous semiconductor, the impurity doped layer is not significantly microcrystalline during the first stage of the film-formation, and
remains amorphous. Since the film-thickness is limited, the impurity doped layer of which only a slight thin part is microcrystallized, exhibits no effect due to microcrystallization. If it is intended to microcrystallize the impurity layer in a sufficient thickness for achieving the desired effects of microcrystallization, the thickness of the impurity layer must be extremely thick, e.g. to an extent of 400 .ANG. (H. Itozaki et al. : Proc. of Int'l. PVSEC-1 pp 707-710 (Nov. 1984)). As a result, since light is now absorbed in the impurity layer, the short-circuit current (I.sub.sc) is reduced. In addition, since the film formed in the first stage is amorphous, the V.sub.oc is reduced.
In order to microcrystallize an impurity doped layer of limited thickness, a special apparatus, such as an apparatus for producing semiconductors by an ECR plasma, is indispensable. However, this is a great hindrance for practical use.